With increasingly use of light-emitting diode (LED) lights, multi-stage switching converters are typically used in order to adjust the brightness of the light sources. In addition, each stage may deal with the power in total, which can increase product costs of the LED drivers. In order to reduce the costs, some conventional techniques divide the secondary winding at the output side of a flyback converter into two groups, and a DC-DC converter of the second stage may be connected to only one of the two groups.